Usually, the bottles on which to apply the labels are positioned along the periphery of a rotary carousel operating machine, at specific plates. One or more operating units are usually present around the carousel designed for operating on the moving bottles to perform predetermined operations such as labelling, filling, application of capsules, etc.
Alternatively, the operating machine may be a machine of the linear type wherein the containers are positioned (and move) along a line (defining a transport path of the containers) which is curved or straight or a set of the two types. In this case, the operating units are positioned along the transport path of the containers.
As regards the labelling unit, it normally comprises a supporting body which extends from a first end to a second end positioned at the operating machine. Also, a prior art labelling comprises means for feeding a web along a movement path, the labels being positioned on the web. More specifically, the feed means are mounted on the supporting body and designed to bring one label at a time to the second end of the supporting body. Usually, the feed means are synchronised with the movement of the carousel in such a way as to bring the label to the bottle, when the latter has reached the second end of the supporting body.
In addition, in the prior art, the labelling unit comprises a detaching unit mounted on the second end of the supporting body and operatively associated with the labels for detaching them from the web in such a way as to bring them into contact with a container in arrival. A specific control unit controls the feed means moving the web along an outward direction in such a way as to bring a respective label to the detaching unit.
In detail, the control unit accelerates the web until the latter reaches a predetermined speed equal to the tangential speed of the container on the carrousel at the detaching unit. In effect, so that the application of the label occurs in the possible best way, the linear speed of the label must be equal to that of the bottle. After reaching the predetermined speed, the control unit controls the feed means to keep the speed constant until the label has entered into contact with the container.
After that, the control unit controls the feed means to decelerate the web until reaching a stop position (or a speed lower than the predetermined speed). In this way, when the next bottle arrives, the system is ready for a new acceleration so as to bring the next label to the bottle, and so on.
Consequently, in the prior art, it is important that the sum of the acceleration space, the deceleration space and the space at a constant speed is equal to “label step” (in this way, the starting position of the labels is the same), where the term “label step” denotes the distance between two successive label fronts of the support. In other words, the label step must include the acceleration space, the movement space at constant speed and the deceleration space.
It should be noted that the term “acceleration space” denotes the space travelled by the web during the acceleration step, the term “deceleration space” denotes the space travelled by the web during the deceleration step, and the term “space at constant speed” denotes the space travelled by the web during the step of moving at a constant speed.
In other words, the control unit is designed for performing a movement cycle for each label of the web. Each movement cycle only comprises the movement of the label along the outward direction for dispensing the label. In more detail, during each movement cycle of a respective label the movement starts from a predetermined initial position. At the end of the cycle (when the movement of the web along the outward direction is finished), the next label is in the initial position relative to the next movement cycle.
The following is provided purely by way of a non-limiting example:                label step=70 mm;        acceleration space=16 mm;        deceleration space=16 mm;        space at a constant speed=70−16−16=38 mm.        
In other words, the sum of the acceleration, deceleration and constant speed spaces is equal to the length of the label step.
Consequently, if the label step is short, there are several drawbacks.
In effect, if the label step is short the acceleration and deceleration spaces reduce as it is necessary to maintain a certain space at a constant speed to allow the application of the label to the moving container.
In other words, under equal conditions of the speed of movement of the carousel (and hence of the bottle), it is necessary to reduce the acceleration and deceleration spaces. For example:                label step=20 mm;        acceleration space=8 mm;        deceleration space=8 mm;        space at a constant speed=20−8−8=4 mm.        
In other words, for moving the label at the predetermined speed of the container, the feed means have available an acceleration and deceleration space which is halved relative to the previous example. This means that, at the same speed of the bottle, the acceleration with which the motor of the feed means must move the support will be four times greater than before (using a law of motion of the support with constant acceleration).
Therefore, in order to apply a very short label the control unit must deal with operating conditions which are at the limit in terms of torque requested from the motor of the means feeding the web. In addition, a fast acceleration and deceleration also results in poor treatment of the web and the mechanics.
More specifically, the greater the acceleration with which the motor moves the web, the greater will be the stresses on the drive rollers about which the web turns.
Also, it should be taken into consideration that the maximum labelling speed for a labelling unit reduces drastically if a very short label must be applied.
In addition, if two labelling units are mounted on an operating machine, one operating on a web with label step equal to 70 mm (for example) and the other operating on a web with label step equal to 20 mm (for example), the maximum production speed of the machine is limited by the maximum labelling speed which can be reached by the unit which applies the 20 mm label.
Alternatively, to overcome the above-mentioned drawbacks, it is possible to increase the label step on a web. This, however, has as a direct consequence that, with the same length of web, fewer labels are present. Consequently, the cost per label is, naturally, higher.